Novel orthogonal modulation format DRZ FSK/DPSK for high speed long haul optical

We propose a novel advanced orthogonal modulation format dark return-to-zero frequency shift keying/differential phase shift keying (DRZ-FSK/DPSK) and its realization scheme. The DRZ-FSK/DPSK is generated by the combination of a 40-Gb/s return-to-zero (RZ) signal and a DRZ signal which is converted from the RZ using a semiconductor optical amplifier (SOA) based on nonlinear cross polarization rotation (XPR) and then re-modulated by high-bit-rate DPSK at 40 Gb/s. The feasibility of the scheme is